Method for producing hydrogen

ABSTRACT

The process for producing hydrogen gas according to the present invention consists of reacting aluminum with water in the presence of sodium hydroxide as a catalyst. In one aspect of the present invention, there is provided a process for producing hydrogen gas, comprising the steps of: providing an aqueous solution containing between 0.26 M and 19 M NaOH in a vessel. The next step consists of reacting aluminum with water at the surface of the solution to generate a region of effervescence at the surface of the solution and a precipitate sinking from the region of effervescence to the bottom of the vessel. The region of effervescence is kept separated from the precipitate at the bottom the vessel, to prevent any precipitate from mixing with the aluminum therein.

This is a Continuation-In-Part of U.S. patent application Ser. No.09/620,250 filed on Jul. 20, 2000, now U.S. Pat. No. 6,506,360.

FIELD OF THE INVENTION

This invention relates to the production of hydrogen gas from thereaction of aluminum with water in the presence of sodium hydroxide ascatalyst.

BACKGROUND OF THE INVENTION

Hydrogen energy is environment-friendly. Because of the actual humanecology concerns, the exploitation of hydrogen as an universal fuelwould be greatly acclaimed. During the last two decades or so, theelaboration of a hydrogen-based economy has made important progress onaccount of numerous research projects such as the hydrogen fuel cell andthe hydrogen car. Although these important discoveries constitutemilestones toward a pollution-free society, more research is needed toobtain the hydrogen easily and economically.

A convenient source of hydrogen is a reaction of aluminum with water tosplit the water molecules into hydrogen and oxygen. The hydrogen isreleased as a gas and the oxygen combines with the aluminum to formaluminum oxide compounds. Aluminum is the third most abundant elementafter oxygen and silicon in the earth's crust, and constitutesapproximately 8% by weight of the earth's crust. Aluminum is a safematerial and is commonly used in the food, cosmetics and medical fields.Water is also abundant. Therefore, the reaction of these two elements toproduce hydrogen represents an interesting proposal to replace fossilfuels.

Generally speaking, it is known that under certain conditions, aluminumreacts with water to generate hydrogen and heat. It is also known,however, that this type of reaction is not sustainable at ambienttemperature. It is believed that a protective oxide layer forms on ametal surface in contact with water at ambient temperature and hindersthe reaction. Therefore, it has been accepted by those skilled in theart that the use of aluminum in a reaction with water to generatehydrogen gas requires that the protective oxide layer is efficiently andcontinuously removed, and that the reaction is kept at an elevatedtemperature.

A number of hydrogen generators have been developed in the past. Thefollowing patent documents constitute a good inventory of the devicesand methods of the prior art in the field of hydrogen gas generationusing the reaction of aluminum or alloys of aluminum with water.

U.S. Pat. No. 909,536 issued on Jan. 12, 1909, and U.S. Pat. No. 934,036issued on Sep. 14, 1909, both issued to G. F. Brindley et al. Thesedocuments disclose several compositions for generating hydrogen. Thecompositions comprise any metal which can form an hydroxide when it isbrought into contact with a solution of a suitable hydroxide. Forexample, aluminum is reacted with sodium hydroxide to release hydrogenand to produce sodium aluminate.

U.S. Pat. No. 2,721,789, issued on Oct. 25, 1955 to Q. C. Gill. Thisdocument discloses the structure of an hydrogen generator for reactingwater with a measured dry charge of aluminum particles and flakes ofsodium hydroxide. The reaction releases hydrogen gas and produces sodiumaluminate.

U.S. Pat. No. 3,554,707 issued on Jan. 12, 1971 to W. A. Holmes et al.This document discloses a gas generator having bellows to raise or lowerthe level of water in response to the pressure inside the generator. Asthe level of water drops, the contact surface between the fuel cartridgeand the water is lost and the reaction is terminated.

U.S. Pat. No. 3,957,483 issued on May 18, 1976 to M. Suzuki. This patentdiscloses a magnesium composition which produces hydrogen upon contactwith water. The preferred magnesium composition comprises magnesium, andone or more metals selected from the group consisting of iron, zinc,chromium, aluminum and manganese.

U.S. Pat. No. 3,975,913 issued on Aug. 24, 1976 to D. C. Erickson. Thisdocument discloses a hydrogen generator wherein molten aluminum isreacted with water. The generator is kept at a very high temperature tokeep the metal in a molten condition.

U.S. Pat. No. 4,643,166 issued on Feb. 17, 1987, and

U.S. Pat. No. 4,730,601 issued on Mar. 15, 1988 both to H. D. Hubele etal. These documents disclose the structure of a fuel cell for producingheat energy and hydrogen gas. The device has a reaction chambercontaining a fuel composition that is reactive with water. The fuelcomposition includes a main fuel part of magnesium and aluminum in amolar ratio of 1:2, and the second part is composed of lithium hydride,magnesium and aluminum in equal molar ratio.

U.S. Pat. No. 4,670,018 issued on Jun. 2, 1987, and

U.S. Pat. No. 4,769,044 issued on Sep. 6, 1988, both to J. H. Cornwell.These documents describe a log made of compressed wood waste and paper.The log is coated with aluminum particles. Upon burning, the aluminumparticles react with moisture in the log to emit heat due to thegeneration of hydrogen gas.

U.S. Pat. No. 4,752,463 issued on Jun. 21, 1988 to K. Nagira et al. Thisdocument discloses an alloy which reacts with water for producinghydrogen gas. The alloy material comprises essentially aluminum and 5 to50% tin.

U.S. Pat. No. 5,143,047 issued on Sep. 1, 1992 to W. W. Lee. Thisdocument discloses an apparatus and a method for generating steam andhydrogen gas. In this apparatus, an aluminum or aluminum alloy powder isreacted with water to generate hydrogen gas. An electric power source isused to start the reaction. The electric power source is used to explodean aluminum conductor and to disperse pieces of molten aluminum into amixture of water and aluminum powder. A heat exchanger is provided toextract useful heat.

U.S. Pat. No. 5,867,978 issued on Feb. 9, 1999 to M. Klanchar et al.This document discloses another hydrogen gas generator using a charge offuel selected from the group consisting of lithium, alloys of lithiumand aluminum. The charge of fuel is molten and mixed with water togenerate hydrogen gas.

JP 401,208,30 issued to Mito on Aug. 22, 1989. This document discloses aprocess for producing hydrogen. Aluminum is reacted with water under aninactive gas or a vacuum to produce hydrogen gas.

CA 2,225,978 published on Jun. 29, 1999 by J. H. Checketts. This patentapplication discloses a hydrogen generation system wherein a coating onreactive pellets is selectively removed to expose the reactive materialto water for producing hydrogen gas on demand. In one embodiment,aluminum and sodium hydroxide are reacted with water to release hydrogengas and produce sodium aluminate.

DE 3,401,194 published in Jul. 18, 1985 by Werner Schweikert. Thisdocument discloses a device for utilizing energy from a chemicalreaction between various aluminum alloys and sodium hydroxide. Thechemical reaction occurring in this device generates heat, hydrogen gas,a direct current and sodium aluminate as a residue.

FR 2,465,683 published in Mar. 27, 1981 by Guy Ecolasse. This documentalso discloses a process for producing hydrogen by the reaction ofaluminum on sodium hydroxide solution in water. A by-product of thisreaction is sodium aluminate.

Belitskus, David. 1970. Technical Note: “Reaction of Aluminum WithSodium Hydroxide Solution as a Source of Hydrogen” J. Electrochem Soc.(1970), (August), Vol. 117. No. 8, pp.1097-9, XP-002180270. Thistechnical paper.describes several experiments wherein aluminum samplesincluding a cylindrical block, uncompacted powders and pellets ofvarious densities have been reacted with aqueous solutions of sodiumhydroxide at various concentrations to generate hydrogen gas. In theseexperiments, the formation of sodium aluminate was observed, as well asthe regeneration of sodium hydroxide through the precipitation ofaluminum hydroxide.

Stockburger, D. et al. 1991. “On-Line Hydrogen Generation from Aluminumin an Alkaline Solution”. Proc.-Electrochem. Soc. (1992), Vol. 92-5(Proc. Symp. Hydrogen Storage Mater., Batteries, Electrochem., pp.431-44, 1992, XP-001032928. This technical paper describes three sizesof hydrogen generators in which aluminum is reacted with an aqueoussolution of 5.75 M sodium hydroxide. This technical paper also notes theformation of sodium aluminate and the precipitation of aluminumhydroxide that regenerates sodium hydroxide.

Although the chemical reactions of aluminum with water in the presenceof sodium hydroxide have been demonstrated in various projects in thepast, these reactions were not considered as being safe for use by thegeneral public. Sodium hydroxide is extremely corrosive and must behandled according to particular safety procedures. Therefore, anychemical reaction wherein sodium hydroxide is a consumable would notrepresent an attractive source of hydrogen for use in vehicles or inhousehold power systems, for examples. As such, it is believed that aneed still exists for a method to produce hydrogen gas by the reactionof aluminum and water, wherein the consumables are limited to aluminumand water.

SUMMARY OF THE INVENTION

Broadly stated, the process for producing hydrogen gas according to thepresent invention consists of reacting aluminum with water in thepresence of sodium hydroxide acting as a catalyst.

In accordance with one aspect of the present invention, there isprovided a process for producing hydrogen gas, comprising the initialstep of: providing an aqueous solution in a vessel. The aqueous solutioncontains sodium hydroxide in a concentration between 0.26 M and 19 MNaOH.

The next step consists of reacting aluminum with water at the surface ofthe solution thereby generating a region of effervescence at the surfaceof the solution and a precipitate sinking to the bottom region of thevessel. The process also includes the step of maintaining the region ofeffervescence separated from the precipitate at the bottom the vessel,to prevent the precipitate from swirling and mixing with the aluminum inthe reaction zone at the surface of the solution. This process isadvantageous because it proceeds catalytically with the sodium hydroxideacting as the catalyst.

The process mentioned above is best carried out with an aqueous solutioncontaining between about 5M and 10 M NaOH. The process is also moreefficient when makeup water is added only after an initial amount ofaluminum has been consumed, and when the temperature of the aqueoussolution has reached a peak or 75° C.

In accordance with another aspect of the present invention, there isprovided a process for initiating and maintaining a catalytic reactionof aluminum with water for producing hydrogen gas. The process comprisesthe initial step of providing an aqueous solution in a vessel. Thisaqueous solution contains a portion of NaOH and a portion of water. Thenext steps consist of introducing a portion of aluminum in the aqueoussolution, and reacting that portion of aluminum with the portion ofwater. The process also includes the steps of maintaining constant theportion of NaOH in the vessel and adding additional portions of waterand additional portions of aluminum in the vessel according to the ratesof consumption of the aluminum and the water in the reaction.

Again, this process is best carried out with an aqueous solution ofbetween 1.2 M and 19 M NaOH and at a temperature between 4° C. and 170°C.

In yet another aspect of the present invention, there is provided aprocess for simultaneously producing hydrogen gas and alumina (Al₂O₃).This process firstly comprises the step of providing an aqueous solutionin a vessel. The aqueous solution contains sodium hydroxide in aconcentration between 0.26 M and 19 M NaOH. The next step consists ofreacting aluminum with water at a surface of the aqueous solution andgenerating hydrogen gas and alumina. The process also includes the stepof recovering hydrogen gas from the surface of the aqueous solution andalumina from a bottom region of the vessel.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description,.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the process according to the present inventionselected by way of examples will now be described with reference to theaccompanying drawings, in which:

FIG. 1 is graph illustrating a first reaction of aluminum with water toproduce hydrogen gas, in a 5.0 M sodium hydroxide solution, carried outover a period of about 130 minutes;

FIG. 2 is a graph illustrating a second reaction of aluminum with waterto produce hydrogen gas, in a 4.95 M sodium hydroxide solution, carriedout over a period of about 100 minutes;

FIG. 3 is a graph illustrating a third reaction of aluminum with waterin a 4.5 M sodium hydroxide solution, while keeping the temperaturerelatively low;

FIG. 4 is a graph illustrating a fourth reaction of aluminum with waterin a 4.5 M sodium hydroxide solution, while keeping the temperaturerelatively low;

FIG. 5 is a graph illustrating a reaction of aluminum with water in a1.2 M NaOH solution;

FIG. 6 is a graph illustrating a reaction of aluminum with water in a2.5 M NaOH solution;

FIG. 7 is a graph illustrating a reaction of aluminum with water in a3.9 M NaOH solution;

FIG. 8 is a graph illustrating a reaction of aluminum with water in a4.8 M NaOH solution;

FIG. 9 is a graph illustrating a reaction of aluminum with water in a5.5 M NaOH solution;

FIG. 10 is a graph illustrating a reaction of aluminum with water in a 6M NaOH solution;

FIG. 11 is a graph illustrating a reaction of aluminum with water in a6.03 M NaOH solution;

FIG. 12 is a graph illustrating a reaction of aluminum with water in a6.1 M NaOH solution;

FIG. 13 is a graph illustrating a reaction of aluminum with water in a 6M NaOH solution, wherein the water was added continuously;

FIG. 14 is a graph illustrating a reaction of aluminum with water in a 6M NaOH solution, wherein the aluminum was added quickly;

FIG. 15 is a graph illustrating a reaction of aluminum with water in a6.7 M NaOH solution;

FIG. 16 is a graph illustrating a reaction of aluminum with water in a11.3 M NaOH solution;

FIG. 17 is a graph illustrating a reaction of aluminum with water in asaturated 19 M NaOH solution;

FIG. 18 is graph illustrating maximum reaction temperatures obtainedwith aqueous solutions of various concentrations, and the responsivenessof the reaction for solutions of various concentrations;

FIG. 19 is a graph showing the effects of adding water to the reactionas, opposed to adding a fixed-molar NaOH solution to the reaction,

FIG. 20 is a partial cross-section view of an apparatus to producehydrogen gas, embodying some of the preferred conditions to carry outthe process according to the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the present invention it is believed that aluminum reacts with waterunder certain conditions in the presence of sodium hydroxide as acatalyst. It is believed that the reaction is carried out according tothe equation (1) or possibly (2), or some combination of the two, asfollows;

2Al+3H₂O→Al₂O₃+3H₂  (1)

catalyst=NaOH

2Al+6H₂O→Al₂(OH)₃+3H₂  (2)

catalyst=NaOH

In one of the most pertinent prior art documents, the U.S. Pat. No.934,036, it is taught that aluminum reacts with water and sodiumhydroxide according to one of the following formulas;

2Al+2NaOH+xH₂O→Na₂Al₂O₄ +xH₂O+3H₂  (3)

2Al+6NaOH+xH₂O→Na₆Al₂O₆ +xH₂O+3H₂  (4)

In other relevant prior art documents, Stockburger and Belitskus teachthat aluminum reacts with an alkaline solution of NaOH and that NaOH issubsequently regenerated by the precipitation of Al(OH)₃ as described bythe formulas (5) and (6) respectively.

2Al+2NaOH+6H₂O→2NaAl(OH)₄+3H₂  (5)

2NaAl(OH)₄→2NaOH+2Al(OH)₃↓  (6)

It is also taught in Stockburger, that an optimum concentration of thealkaline solution should be maintained at 5.75 M NaOH for an acceptablereaction rate, and in Belitskus that the rate of precipitation ofAl(OH)₃ and the regeneration of NaOH is insufficient to support rapidreaction rates.

The following experiments were carried out to demonstrate that undercertain conditions, the sodium hydroxide is not consumed in the reactionbut acts as a catalyst to the reaction as described in equation (1) or(2).

Experiments 1-1 to 1-8

A first series of eight experiments was carried out to measure thevolume of hydrogen gas produced in a typical reaction. In theseexperiments, aluminum foil from Reynolds Aluminum Company of Canada wasloosely crumpled and placed in a one liter plastic bottle containing 500ml of catalytic solution of about 4.5M NaOH. The bottle was quicklycapped with a cover fitted with a tube which led to an invertedvolumetric cylinder filled with water. The bottle was immersed in awater bath to prevent overheating.

The volume of water displaced by the gas produced was measured andcorrected to a gas volume at standard temperature and pressure (STP).Atmospheric pressure on that day was obtained from a local weatheroffice. The corrected volume of gas produced was compared to thetheoretical quantity of hydrogen gas, which would be obtained accordingto the equation,

2Al+3H₂O→Al₂O₃+3H₂  (1)

These experiments were carried out at a room temperature of 21° C. andan atmospheric pressure of 758 mm of Hg. In all cases the reactionstarted in few seconds and continued for few minutes, until depletion ofthe aluminum foil. It was noticed that a typical reaction with less than5 grams of loosely crumpled aluminum foil, is complete in less than 5minutes. The results of these experiments are shown in Table 1 below.

TABLE 1 Hydrogen Gas Production from Aluminum Foil Exp. Al H₂ H₂ (l) H₂(l) Yield Deviation (#) (g.) (l) (STP) Theoretical (%) (+/− %) 1-1 2.082.94 2.71 2.59 104 2.6 1-2 2.03 2.85 2.62 2.53 104 2.6 1-3 2.21 3.052.81 2.75 102 2.5 1-4 2.16 2.9 2.67 2.69 99 2.6 1-5 2.2 3.04 2.8 2.74102 2.5 1-6 2.21 3.04 2.8 2.76 102 2.5 1-7 0.73 1.03 0.94 0.91 103 2.41-8 0.83 1.15 1.05 1.03 102 2.2 Ave. 102 2.47

The results from Table 1 show that the reaction is reproducible andproduces stoichiometric quantities of hydrogen gas. The 102% averageyield of hydrogen gas is considered to be within the measurementuncertainty; however, there are at least two factors which might havecontributed to a slightly higher hydrogen yield. Firstly, the volume ofgas produced was corrected to STP. It is possible that the exhaustedfume hood in which the experiments were carried out could have loweredthe reaction pressure below the atmospheric pressure of 758 mm of Hg.This would have increased the observed value for the volume of gasproduced. An exhaust bench typically runs at 1 inch or 2 inches of waterpressure. At a maximum, this could have increased the measured volume byabout 0.5%.

Secondly, the water used was tap water in all cases, in which dissolvedair may have been present. If any of this air had been released in thepresence of the warm hydrogen gas, this would have increased the volumeof gas; measured. This would have affected the results by less than 1%.Since the results are within the measurement error, and quantificationof these two sources of error would not significantly affect theresults, no further experiment was carried out in this area.

Experiments 1-9 and 1-10

The procedure used in the above experiments was repeated, with theexception that the tube leading from the top of the reaction bottle wasconnected to a gas sampling bag. Two samples of gas were obtained and,analysed. The results are presented in Table 2.

TABLE 2 Gas Analysis Hydrogen Oxygen & Sample Concentration Nitrogen 1(1-9) 92% balance 2 (1-10) 98% balance

Table 2 shows that the purity of the hydrogen collected in the secondsample was 98%. This is close to what was theoretically expected. Thelower 92% concentration observed in the first sample was probably due tothe fact the system was not completely purged with hydrogen before thesample was taken. By the time the second sample was taken, most of theair had been purged from the tube and the reaction bottle.

Experiment 1-11

The procedure used in the first mentioned experiments was repeatedexcept that the reaction bottle was placed in a water bath before thealuminum was added to the water, and the hydrogen produced was bubbledthrough the bath water. The temperature of the bath and the catalyticsolution were measured before and after the reaction, and at about fourminutes after the reaction was completed.

The water equivalent of the plastic containers for absorbing heat andtheir specific heat were determined experimentally by adding a knownquantity of hot water to the reaction system at room temperature andthen calculating the heat transfer based on the final temperature.

The quantity of heat produced by the reaction was determined andcompared with the theoretical values. The results are shown in Table 3.

TABLE 3 Heat of the Reaction Temp. Temp. ° C. Temp. ° C. Temp. ° C. ° C.Reactor Bath Reactor Bath Readings Start Start Finish Finish Time 1(1-11) 21.1 20.2 45.5 24.4 5.29 2 (1-11) 21.1 20.2 38.3 25.3 5.33 HeatHeats of Heat of Heat Output Formation Formation Output Theo- Effi- AlAl₂O₃ H₂O Actual retical ciency Readings (g) kcal/mole kcal/mole kcalkcal (%) 1 (1-11) 9.52 −400.5 −68.3 33.3 34.5 96 2 (1-11) 9.52 −400.5−68.3 32.5 34.5 94

The results in Table 3 show that the observed heat released in theproduction of hydrogen was 96% of the theoretical value. The 94% valuefrom the second reading can be attributed to the heat lost to thesurroundings during the time that lapsed between the readings.

The reaction has a net maximum heat production during hydrogengeneration of 195.6 kCal/mole. A further 204.9 kCal/mole will bereleased if the hydrogen is burned with oxygen. Stated another way, 51%of the reaction energy is used to form hydrogen gas and 49% goes intothe production of heat.

Experiment 2-1

With 5.00 M NaOH Alkaline Solution

Sodium hydroxide (NaOH) pellets (40.63 g) from Wiler Fine Chemicals wereplaced in a two liter Erlenmeyer flask. Tap water (200 ml) was added tothe flask. The mixture was swirled and allowed to stand on the labbench. The lab temperature was 25° C. After about an hour, aluminum (Al)foil (30.72 g) was added in two portions. The first addition of aluminumis referred to as time zero, the start of the reaction. The temperatureof the vapour coming from the top of the flask was measured using athermometer and was found to be 93° C. four minutes after the first halfof the Al had been added. The flask was open to the atmosphere. Thereaction was carried out for a period of 130 minutes. Additionalquantities of Al and water were added at regular intervals, and thetemperature was observed and recorded. The flask was swirledperiodically to ensure the solution was in contact with the Al. Nofurther NaOH was added.

During this first experiment, a total amount of 98.7 g of aluminum wasadded, and 650 ml of water was added to the initial volume. A graphicillustration of this Experiment 2-1 is shown in FIG. 1. In thisillustration, the heavy curve labelled as ‘T’ indicates the temperatureof the vapour coming out of the flask; the medium density curve labelled‘A’ indicates the amount of aluminum added; and the lighter curve ‘W’indicates the water added. The same labelling is used for all theexperiments illustrated herein.

The addition of Al to the NaOH solution resulted in the production ofvapour which issued from the neck of the flask at temperatures above 90°C. Furthermore, this production of hot vapour started within a fewminutes (less than 4 minutes) of the Al being added. The reactionproceeded vigorously with the addition of each charge of Al.Furthermore, even when there was a delay between charges, such as at the36 minute and 44 minute additions, the reaction proceeded. Indeed, evenwhen the addition of Al was delayed for 41 minutes and the reactionmixture had been allowed to cool, the reaction still proceededvigorously (at about 128 minutes) when Al was added and the mixture wasswirled.

It is to be noted that the amount of aluminum consumed in this reactionis about 3.6 times the amount predicted by the formulas (3) and (5), andabout 10.8 times the amount predicted by the equation (4). Thesefindings confirm the catalytic nature of the reaction according to thepresent invention.

Experiment 2-2

With 4.95 M NaOH Alkaline Solution.

To tap water (100 ml) in a one liter suction flask was added NaOHpellets (20.12 g) from Willer Fine Chemicals. The mixture was swirled toaid solvation. The lab temperature was 23° C. Two thermocouples wereinserted through the suction inlet on the flask. The flask was open tothe atmosphere. Thermocouple 1 (TC1) was placed in the NaOH solutionabout one centimeter from the bottom of the flask. The junction ofthermocouple 2 (TC2) was placed in the flask neck at the same level as,the suction inlet. The thermocouples were read by a Scimetric System 200data recorder which stored the temperature readings at five secondintervals. After about half an hour TC1 and TC2 read 31° C. and 21° C.respectively After 53 minutes, TC1 and TC2 read 26° C. and 22° C.,respectively, and heavy duty Al foil (4.90 g) from Alcan AluminumLimited was added to the solution. There was vigorous reaction. This isreferred to as time zero, the start of the reaction.

After four minutes, water (35 ml) was added to the solution. Al foil andwater were added at five minutes intervals. The flask was swirledperiodically. No further NaOH was added. FIG. 2 illustrates the responseof this reaction in Experiment 2-2.

The reaction was monitored for about 90 minutes. During that period atotal of 53.32 grams of aluminum was consumed and 350 ml of water wasadded to the initial quantity. The quantity of aluminum addedcorresponds to about 3.9 times the amount predicted by formulas (3) and(5), and about 11.8 times the amount predicted by equation (4). Againthis confirms that the reaction according to the present inventionproceeds according to equation (1) or (2). In this experiment, there wasno occasion in which Al was added that the temperature of the vapourbeing emitted did not increase two to three minutes of the Al beingadded. A sharp drop in the temperature was observed about one minuteafter the addition of water. This is to be expected since the water wasat room temperature (˜23° C.) and it was poured in through the top ofthe flask. Thus, it would cool the system momentarily.

In both Experiments 2-1 and 2-2, there was no indication that thereaction would not have proceeded indefinitely if more Al had beenadded. The regular addition of Al and the fact that the temperature ofthe vapour remained above 80° C., except when water was added, indicatethat the reaction proceeded directly and no time was there a pause inthe reaction to permit the regeneration of any reagent species aspredicted by the formula (6).

The following Experiments 2-3 and 2-4 were carried out at temperature of45° C. or less to determine whether the reaction would be sustainable atthese temperatures. The composition of the precipitate forming in thereaction at these temperatures, as well as the composition of the gasesemitted were also analysed.

Experiment 2-3

Collection of Precipitate at an Early Stage of the Reaction

Sodium hydroxide (NaOH) pellets (39.92 g) from Wiler Fine Chemicals, Lot#14449, were placed in a two liter Erlenmeyer flask. Tap water (182 ml)was added to the flask. The mixture was swirled and allowed to stand onthe lab bench over night. Then it was swirled again to dissolve theremaining NaOH and mix the solution. The solution was then transferredto a 400 ml beaker.

Commercial aluminum foil (24.23 g), namely Reynolds Wrap™, a RegisteredTrade Mark of Canadian Reynolds Metal Company, Ltd., was>weighed,folded, and cut into portions that ranged in weight from 0.5 g to 1.5 g.The beaker containing the NaOH solution was placed in a water bath whichwas cooled with ice cubes. Thermometers were placed in both the waterbath and the beaker. Care was taken to ensure the temperature of thesolution in the beaker was kept at or below about 45° C. In each case,the temperatures of the solutions were read and recorded just before theportions of Al were added. At 29, 44, and 50 minute the reaction beakerwas removed from the water bath to try to keep the reaction temperatureas close to 45° C. as possible.

The Al foil was added in portions over a 59 minute period. When the Alwas added to the initial reaction mixture, gas bubbles were observed toform after about 45 seconds. It was noted that when gas bubbles formedon the surface of the Al, the piece of Al floated at or near the top ofthe reaction mixture. A small amount of fine black material was observedto float in the reaction mixture after all the Al has been dissolved. Bythe 44^(th) minute, the reaction mixture was observed to be very viscousbecause of the formation of a solid material. At 50 minute, tap water(30 ml) was added to the reaction mixture. This Experiment 2-3 isexplained graphically in FIG. 3.

The solution was allowed to cool to room temperature, then it wasfiltered through a porcelain suction funnel without any filter paper toensure there was no un-reacted Al present in the reaction mixture whichcould distort the analysis of the precipitate. The cloudy, grey, viscousmaterial which passed through the funnel was filtered using a papertowel. It was washed with tap water. The final precipitate, a light greysolid, was allowed to stand in the fume hood overnight, then a portionof it, labelled P3-1, was dried in an oven at 102° C. After 45 minutesthe sample was sealed in a plastic bag and taken to an ElectronMicroscopy Unit for analysis. The results of this analysis are presentedin Table 4.

Experiment 2-4

Collection of Precipitate at an Advanced Stage of the Reaction

A 400 ml beaker containing tap water (175 ml) in which NaOH pellets(38.11 g) had been dissolved was placed in a water bath which was cooledby ice cubes. Al foil (39.26 g) was weighed, folded and cut intoportions ranging up to 2 g. Both the NaOH and the Al came from the samesource as described in Experiment 2-3. The Al foil was added to the NaOHsolution over a 148 minute period following the same procedure as inExperiment 2-3. Additional water, totalling 70 ml, was added in fourportions during the Experiment 2-4 at the times shown in FIG. 4.

The reaction mixture was allowed to stand in the fume hood for about twohours after the addition of the last portion of Al, by which time themixture had stopped bubbling. Part of the mixture was then filteredthrough a fine plastic mesh to ensure no un-reacted Al could contaminatethe sample to be analysed. The mixture which passed through the mesh wasthen filtered by suction using qualitative filter paper. A sample ofthis grey precipitate was taken without washing and labelled P4-1. Theremainder of the precipitate was removed from the filter paper andswirled with tap water in a flask, then it was re-filtered and washedwith tap water.

A sample of the washed precipitate was taken and labelled P4-2. Bothsamples were dried in an oven at 102° C. for about an hour then theywere sealed in a plastic bag and taken to the Electron Microscopy Unitfor analysis. The results of the analysis are given in Tables 5 and 6.

The samples taken from Experiments 2-3 and 2-4 were analysed using aJEOL-6400 Scanning Electron Microscope (SEM) equipped with a Link eXLx-ray microanalyser. An accelerating voltage of 15 kV and a probecurrent of 1.5 nA were employed, and spectral collection times were 200sfor sample P3-1 and 120s for samples P4-1 and P4-2. The results are;reported as oxide weight percent values, although oxygen was notanalysed. Oxide values were calculated from elemental analyses usingspecified oxide stoichiometries. The minimum detection limits for NaOHunder these conditions are approximately 0.38 wt. % for sample P3-1 and0.5 wt. % for samples P4-1 and P4-2.

TABLE 4 Sample P3-1. SiO₂ n.d. n.d. 0.23 0.32 0.18 TiO₂ n.d. n.d. n.d.n.d. n.d. Al₂O₃ 59.71 67.63 80.08 57.50 70.11 FeO 0.27 0.28 0.33 0.300.44 MnO n.d n.d. n.d. n.d. n.d. MgO n.d. n.d. n.d. n.d. n.d. CaO 0.260.28 0.35 0.41 0.18 Na₂O 0.39 n.d. n.d. n.d. n.d. K₂O n.d. n.d. n.d.n.d. n.d. CuO 0.38 0.46 0.42 0.70 0.41 Total 61.01 68.65 81.41 59.2371.32 n.d. = not detected

TABLE 5 Sample P4-1. SiO₂ 0.21 0.27 n.d. n.d. n.d. TiO₂ n.d. n.d. n.d.n.d. n.d. Al₂O₃ 63.05 54.87 62.40 63.02 74.57 FeO 0.26 0.26 n.d 0.290.32 MnO n.d n.d. n.d. n.d. n.d. MgO n.d. n.d. n.d. n.d. n.d. CaO n.d.n.d. n.d. n.d. n.d. Na₂O 8.03 11.21 9.46 4.02 4.25 K₂O n.d. n.d. n.d.n.d. n.d. CuO n.d. n.d. n.d. 0.37 n.d. Total 71.55 66.61 71.86 67.7079.14 n.d. = not detected

TABLE 6 Sample P4-2. SiO₂ n.d. 0.29 n.d. n.d. 0.22 TiO₂ n.d. n.d. n.d.n.d. n.d. Al₂O₃ 70.96 72.01 63.77 69.72 65.80 FeO 0.30 0.35 0.32 0.230.28 MnO n.d n.d. n.d. n.d. n.d. MgO n.d. n.d. n.d. n.d. n.d. CaO 0.180.10 0.16 n.d. 0.14 Na₂O n.d. 0.69 n.d. n.d. n.d. K₂O n.d. n.d. n.d.n.d. n.d. CuO 0.42 0.37 0.30 0.42 0.51 Total 71.86 73.81 64.55 70.3766.95 n.d. = not detected

The results presented in Tables 4-6 show the precipitate formed does notcontain sodium beyond what could reasonably be expected to be present inan impure material precipitated from a concentrated NaOH solution. In nocase was the quantity of sodium in the precipitate present in amountsexceeding 1.1% of that required by the reaction products specified inequation (3), (4) or (5). Therefore it may be concluded that theprecipitate formed is not Na/Al moiety, but is rather primarily anAl/Oxygen material, which may contain some hydrogen in the form ofhydroxyl groups or water molecules.

The two samples collected and analysed in Experiment 2-4 show twothings, namely, the washing of the precipitate with water removessignificant amounts of Na; and that none of the five measurements on theunwashed precipitate showed levels of Na which exceeded more than 34% ofthat necessary to form the compounds given in equation (3), (4) or (5).Indeed, the average sodium content of the five measurements was lessthan one-fifth of that necessary to form the compounds given in equation(3), (4), or (5). This removes any possibility that the Na/Al substancesas shown in equation (3), (4) or (5) was at one time present in thereaction precipitate and was subsequently changed to an aluminum/oxygenspecies by washing. If such were the case the Na:Al ratio from sampleP4-1 would have had to be at least 1:1. This was not observed.Therefore, it may be concluded that even in the unwashed state theprecipitate is primarily an aluminum based compound.

The fact that washing with water readily removes most of the sodiumconfirms that the sodium species present is water soluble as would beexpected for an ionic species containing sodium.

Experiment 2-5

Activeness of the Filtrate

To a small amount (˜50 ml) of the filtrate from the first filtration inExperiment 2-4, was added Al foil (0.5 g). Within about 60 seconds,bubbling started and the Al completely dissolved, and a grey precipitateformed in this previously clear solution.

Experiment 2-6

Collection of Gases.

To tap water (182 ml) in a four liter plastic bottle was added NaOHpellets (40.15 g). The bottle was covered, shaken and-the solutionallowed to come to room temperature after the NaOH had dissolved. Thebottle was then placed in a water bath at 18° C. Al foil (14.8 g) wasadded in three portions of about 5 g each. Both the Al and NaOH camefrom the same source as described in Experiment 2-3. After the firstportion of Al (4.63 g) was added, the bottle was capped with a lidfitted with a hose. Bubbles started to form on the surface of the Alafter about 10 seconds. Bubbles came out of the hose, which wassubmerged in the water bath, after about 40 seconds. The Al hadcompletely reacted within about three minutes. The lid was removed fromthe bottle and a second portion of Al foil (4.98 g) was added and thebottle recapped. Bubbling from the hose started after about 30 seconds,the hose was connected to a gas sampling bag and sample P6-1 wascollected. The addition of Al foil (5.19 g) was repeated and gas sampleP6-2 was collected. Both gas samples were analysed. The analytic dataand the normalized results are summarized in Table 7.

TABLE 7 Gas Analysis. Observed Normalized Concentrations ConcentrationsSample # P6-1 P6-2 P6-1 P6-2 Oxygen 2% 1% 2% 1% Nitrogen 7% 2% 7% 2%Hydrogen 86% 92% 91% 97% Total 95% 95% 100% 100%

Experiments 3-1 to 3-15

A series of fifteen experiments was carried out using NaOHconcentrations which ranged from about 0.25M to a saturated solution ofNaOH in water at room temperature. The saturated solution was about 19M.Thirteen of these experiments were recorded on graphs, and are shown inthe accompanying FIGS. 5-17. On these graphs, the labels ‘T’, ‘A’ and‘W’ designate the temperature of the reaction, and the aluminum andwater added respectively as in the previous graphs. The label ‘S’ hasbeen added, however. The line ‘S’ across each graph designates theamount of aluminum that would react with the initial amount of NaOH ifthe reaction would proceed according to the equation (3), (4) or (5).This amount is also referred to herein as the stoichiometric amount ofaluminum.

Solutions of NaOH were typically cooled before starting the reactions.The starting temperature for each reaction was often in the range of4-10° C. The reactions were carried out in glass vessels ranging in sizefrom 25 ml to 500 ml. Solutions of NaOH were prepared by dissolving NaOHpellets from BDH Inc., Toronto, Ontario, Canada, M8Z 1K5, Lot#128142-125228, in tap water at room temperature. The heat of solvationwas allowed to dissipate and the portion of the solution to be used inthe experiment was cooled in an ice bath in the reaction vessel.

A thermocouple junction was placed in the solution about one centimeterbelow the surface. The thermocouple reading was monitored continuallyand recorded on a computer file every 15 seconds.

Aluminum foil (Reynolds Wrap from Canadian Reynolds Metals Company Ltd.,Montreal, Toronto, Calgary, Canada) was crumpled or folded and added inportions ranging from 0.2 g to 1.1 g. Each portion of Al foil wasinitially submerged in the solution using a glass stirring rod. Then itwas allowed to float to the top of the solution. The start time forevery experiment was the time when the first aluminum was added.Aluminum was added in amounts to keep the temperature above 60° C.

Water was added in amounts up to 20 ml. Water was only added when thereaction mixture became viscous and foamed more than one centimeter. Inmost of the experiments, the addition of water started after about 75%of the stoichiometric amount of Al was added. Water was added insufficient quantities to ensure that the level of the solution was atleast one centimeter above the level of the precipitate. In most cases,water was added only after the temperature had reached a peak or a valueof at least 75° C. The portions of water were also controlled so thatthe temperature of the top of the solution did not drop more than 60° C.when the water was added. Aluminum and water were added until at leasttwo times the stoichiometric amount, based on equation (3), had beenreached.

After the reaction had ceased the solution was cooled and theprecipitate was suction-filtered, and rinsed while still in the suctionfunnel with about 250 ml of tap water. Samples from the Experiments 3-1to 3-15 were sent for elemental analysis of the precipitate and thehydrogen gas. The results of these analyses are shown in Table 8.

TABLE 8 Catalytic Ratios and Product Analysis. [NaOH] Catalytic [Al₂O₃][Na₂O] H₂ Test (#) (M) Ratio (%) (%) (%) 3-1 0.26 3.0 98.3 <0.71 3-20.60 3.1 98.9 <0.71 3-3 1.2 4.2 96.3 1.14 3-4 2.5 3.3 98.7 0.7 3-5 3.93.9 96.8 <0.71 3-6 4.8 3.4 3-7 5.5 4.5 98.6 <0.71 3-8 6.0 2.6 3-9 6.03.3 98.6 <0.71 97 3-10 6.1 4.2 3-11 6.1 3.2 99.3 <0.71 3-12 6.1 3.8 98.3<0.71 3-13 6.7 3.3 99.1 <0.71 3-14 11.3 2.7 97.3 <0.71 98 3-15 19 2.799.1 0.79 97

The expression “catalytic ratio” in the above table is calculated bydividing the amount of Al that actually reacted by the amount that wouldhave reacted if the reaction were stoichiometric with respect to NaOH asin equation (3), (4) or (5).

Table 8 also shows the results of the analyses of the precipitatesfiltered from twelve of the experiments. In every case the concentrationof the Al species is larger than 96%. Sodium was detectable in onlythree of the samples, and then at a maximum concentration of only 1.14%or less. Thus, aluminum is present in the precipitate at levels that aretwo orders of magnitude above sodium.

It may be concluded that the reaction according to the present inventionis catalytic in aqueous solutions from 0.26 M NaOH to 19 M NaOH. Itshould be noted that although the 0.26 M and 0.60 M solutions showed acatalytic reaction, the reaction temperature did not rise above 30° C.during those experiments. However, FIG. 5 shows that the temperature ofthe 1.2 M solution rose above 45° C. even though the Al was added veryslowly and only after the previous portion had dissolved.

The results in FIGS. 5-17 show that the reaction can and does occur overa temperature range from 4° C. to 165° C. In one experiment with thesaturated solution a temperature of 170° C. was observed. The molalboiling point elevation constant will result in a higher boiling pointfor the more concentrated solutions, ensuring that water does not boiloff until the higher boiling point is reached. In the case of thesaturated solution from Experiment 3-15, the boiling point elevationwould have contributed to the high boiling point of the solution. It wasalso noted that NaOH did not precipitate from the solution even at thehigher concentration, probably because of the known higher solubility ofNaOH in hot aqueous solutions.

It was found that at about 75% of the stoichiometric amount the solutionwould become viscous and foaming with large longer-lasting bubbles.Water was added at this point and often the addition of Al had to beslowed down or an excess of un-reacted aluminum could be observed.

The formation of a greyish-white precipitate would start between 75% and100% of the stoichiometric amount. Once the precipitate started to formit was necessary to keep the reaction zone above the precipitate adistance of about I cm, or the precipitate would mix with the bubblingaluminum and form a more viscous foam which on occasion overflowed thereaction vessel.

Based on all the experiments described herein, it will be appreciatedthat the present process to produce hydrogen is reproducible withaqueous solutions from 1.2 M NaOH to 19 M NaOH and over a temperaturerange from 4° C. to greater than 170° C. Furthermore, the reaction iscatalytic over the same temperature range and over a NaOH concentrationrange of 0.26 M to above 19 M. The reaction's by-product compriseshigh-purity alumina (Al₂O₃).

Referring now to the graph in FIG. 18, there is shown therein a firstcurve 30 showing the maximum temperatures obtained with different NaOHconcentrations. This best-fit curve was plotted from the data shown inFIGS. 5-17, and is presented herein for illustrating the effect of NaOHconcentration on the maximum temperature of the reaction. FIG. 18 showsanother curve 32 which represents the responsiveness of the reaction toaluminum and water additions. This curve has been prepared by plottingthe time required to reach the initial maximum temperature of thereactions, against the different NaOH concentrations studied. Theresulting best-fit curve is a complex inverted hyperbolic curve centredon a concentration of about 8 M NaOH. This curve indicates that thereaction is highly responsive to fuel additions, when the NaOHconcentration is between about 5 M and 10 M, and that the responsivenessdecreases rapidly when the NaOH concentration is adjusted away from thismedian region.

Referring now the FIG. 19, there is illustrated therein two curves. Thefirst curve 34 represents the effect of adding plain water to thecatalytic reaction of equation (1) or (2). As the reaction proceeds, thewater is consumed, and therefore, the concentration of NaOH increases,as shown by the segment: 36, from its initial concentration 38. Whenwater is added, as indicated by segment 40, the concentration drops backto or below the initial concentration 38. If water is added in portionsto maintain a certain level in a reaction vessel for example, thesolution concentration fluctuates up and down from the initialconcentration 38, as generally represented by the curve 34.

If someone is led to believe that the reaction proceeds as in equation(3), (4) or (5), that person would logically add NaOH into the reactionvessel with the makeup water. If NaOH is added to a reaction thatactually proceeds according to equation (1) or (2), however, theresulting NaOH concentration of the aqueous solution in the reactionvessel would increase as represented by curve 44. Whether the NaOH isadded alone or in a fixed-molar NaOH solution, as represented by segment46, the NaOH concentration of the solution in the reaction vessel wouldmove quickly toward saturation.

Reference is made again to the curve 32 in FIG. 18. It will beappreciated that a regular addition of a fixed-molar NaOH solution to areaction that proceeds according to equation (1) or (2) would cause theresponsiveness of the reaction to move along the curve 32 as indicatedby the series of arrows 48, and quickly reach a region of very lowresponsiveness. Such migration of the NaOH concentration toward a regionof low responsiveness would cause the reaction to cease or to appear tohave ceased. The addition of plain water, however, as taught herein,causes the responsiveness of the reaction (1) or (2) to oscillate backand forth along the curve 32 toward and away from a more reactive state,as shown by arrows 50 and 52. These oscillations 50, 52 are believe tostimulate the reaction, and to contribute to some degrees to thecatalytic feature of the reaction according to the present invention.

The arrows 50, 52 and the corresponding theory explain the facts that insome experiments, a water addition has caused the reaction to slow down,according to the arrow 50, and in other experiments, the addition ofwater caused an immediate response, as in 52. The same theory explainswhy both events can occur in a same experiment, such as when the NaOHconcentration is maintained substantially in the median region, between5 and 10 M NaOH. The curve 44 and arrows 48 on the other hand, explainwhy prior inventors may have failed to observe a catalytic reaction withthe same elements.

It has been found that the reaction proceeds better when water is addedafter an initial amount of aluminum has been consumed. This phenomenoncan also be explained using the curve 32 in FIG. 18. In a lowconcentration solution, any delay in adding water causes the NaOHconcentration to move toward a highly responsive state, such as around8M for example. An addition of water at that time and a subsequentaddition of makeup water causes the NaOH concentration to oscillatewithin this highly responsive region. On the other hand, if the initialconcentration is above 8 M for example, an addition of water brings theconcentration back to a highly responsive state, and therefore immediateresults can be observed.

Additional Experiments

Additional experiments were carried out using aluminum wire of differentgauge sizes and aluminum flakes from the helical casing of armouredelectrical wire. Although these additional experiments were not recordedin details, the catalytic effect was observed. Therefore, it is believedthat the reaction (1) or (2) is reproducible with aluminum flakes frombeverage cans and food packages, aluminum chips, shavings and sawdustfound in machine shop waste, and aluminum powder available commerciallyfor different purposes including fireworks, or other small aluminumparticles of the like. It is to be expected that the intensity of thereaction depends upon the surface of contact between the aluminum andwater. Aluminum foil for example reacts faster than a heavy gaugealuminum wire, and aluminum powder would react almost instantly toproduce hydrogen gas.

Preferred Apparatus

A preferred hydrogen generator 60 is illustrated in FIG. 20. Thehydrogen generator 60, comprises a reaction vessel 62 made ofnon-corrosive material, in which the reaction is carried out. A minimumamount of an alkaline solution 64 is maintained in this vessel. Duringthe operation of the generator, it has been found that aluminumparticles reacts with water at the surface 66 of the alkaline solutionand defines at and near the surface 66, a region of substantialeffervescence. This region is defined as the reaction zone ‘F’. Theheight of the reaction zone ‘F’ vary with the intensity of the reaction,and extends above and below the surface 66 of the alkaline solution 64.During the operation of the generator, a precipitate 68 accumulates atthe bottom of the reaction vessel 62. It is recommended to maintain thereaction zone ‘F’ at a height ‘H’ of at least about 1 cm above theprecipitate 68, to prevent the precipitate from swirling into thereaction zone and mixing with the aluminum particles. Although thisdimension can be reduced in some installations, a dimension of onecentimeter is suggested herein to enable those skilled in the art toreadily use the process according to the present invention successfully.

A water bottle 70 is affixed to the side of the reaction vessel 62 andhas a piping system 72 connected to an array of nozzles 74 in the bottomof the reaction vessel 62. Only one nozzle is shown for clarity. Theintroduction of water through the bottom of the vessel 62 has the effectof capturing some of the heat in the precipitate 68 to preheat the waterentering the reaction vessel. A second purpose for the feeding of waterthrough the bottom of the reaction vessel 62 is to entrain to thereaction zone ‘F’, any sodium hydroxide which may be present in theprecipitate 68.

While the distance ‘H’ of the reaction zone ‘F’ above the precipitate 68defines a low limit to the water content in the reaction vessel, theupper limit should be defined as to maintain the concentration of thealkaline solution over about 1M NaOH, and more preferably, aconcentration of 5M NaOH. A sight glass 76 on the side of the reactionvessel 62 is provided to monitor the minimum distance ‘H’ of thereaction zone ‘F’ above the precipitate 68.

Aluminum particles 78 are delivered into the reaction vessel 62 from ahopper 80 mounted on the top of the vessel 62, though an airlock™ rotaryfeeder 84 and through a drop pipe 86 at the center of the reactionvessel 62. A deflector 88 is mounted at the end of the drop pipe 86 todisperse the aluminum particles 78 over the entire surface of thealkaline solution 64. The hydrogen generated in the reaction vesselexits through the drop pipe 86 and the spout 90.

The drop pipe 86 is preferably mounted through a large openable cap 92on the top of the reaction vessel. This cap 92 preferably covers asubstantial portion of the upper end of the reaction vessel 62 andprovides access to the reaction vessel for periodically cleaning thevessel. A bung 94 is provided in the bottom surface of the reactionvessel 62 to recover the precipitate 68.

The aluminum particles 78 are preferably flakes, sawdust, millingshavings and chips, powder or other similar small particles having alarge surface over volume ratio. It has been noticed that aluminum foilfragments for example, have a tendency to float at the surface 66 of thealkaline solution 64. This is preferable and is explained by thebuoyancy created by the foam 96 and the bubbling action generate in thereaction zone ‘F’. It is believed that the bubbling action and the hightemperature in this reaction zone is ideal to prevent or reduce theformation of a protective oxide layer on the surface of the aluminumparticles. It is believed that the retention of the aluminum particlesin this reaction zone contributes largely to maintaining the catalyticeffect.

When relatively dense aluminum particles are used, it is recommended toinstall a floating screen 98 at the surface of the alkaline solution 64,to retain the aluminum particles in the reaction zone ‘F’.

As to other manner of usage and operation of the process according tothe present invention, the same should be apparent from the abovedescription and accompanying drawings, and accordingly furtherdiscussion relative to these aspects is deemed unnecessary.

We claim:
 1. A process for producing hydrogen gas, comprising the stepsof: providing an aqueous solution in a vessel, said solution containingbetween 0.26 M and 19 M NaOH; introducing aluminum in said solution;reacting aluminum with water at a surface of said solution therebygenerating a region of effervescence at said surface of said solutionand a precipitate; and while effecting said step of reacting, forming anaccumulation of precipitate at a bottom region of said vessel,separating said region of effervescence from said accumulation andpreventing precipitate from said accumulation from mixing with aluminumreacting with water in said region of effervescence.
 2. The process asclaimed in claim 1, wherein said steps of separating and preventinginclude the step of maintaining said region of effervescence at adistance of about 1 cm above said accumulation of precipitate.
 3. Theprocess as claimed in claim 1, wherein said aqueous solution containsbetween about 5M and 10 M NaOH.
 4. The process as claimed in claim 1,further comprising the step of causing a NaOH concentration in saidaqueous solution to oscillate equal amounts up and down.
 5. The processas claimed in claim 1, further comprising the step of causing a NaOHconcentration in said aqueous solution to oscillate equal amountsbetween about 5M and 10M NaOH.
 6. The process as claimed in claim 1,wherein said step of reacting aluminum with water at a surface of saidsolution comprises the additional step of retaining said aluminum on afloating screen.
 7. The process as claimed in claim 1, furthercomprising the step of; adding water and aluminum in said vesselaccording to a rate of consumption of said aluminum and said water insaid step of reacting.
 8. The process as claimed in claim 7, whereinsaid step of adding water and aluminum in said vessel is carried out insequence, with said aluminum being added first.
 9. The process asclaimed in claim 8, wherein said step of adding water is carried outwhen a temperature in said aqueous solution has reached a peak or 75° C.10. The process as claimed in claim 1, wherein said precipitatecomprises alumina, and further comprising the step of recovering saidalumina.
 11. The process as claimed in claim 1, wherein said step ofseparating said region of effervescence from said accumulation comprisesthe step of adding water to said solution.
 12. A process for producinghydrogen gas, comprising the steps of; providing an aqueous solution ina vessel, said aqueous solution containing a portion of NaOH and aportion of water; introducing a portion of aluminum in said aqueoussolution; reacting said portion of aluminum with said portion of water,thereby producing hydrogen gas; and while effecting said step ofreacting, maintaining constant said portion of NaOH in said vessel,adding additional portions of water and additional portions of aluminumin said vessel according to a rate of consumption of said portion ofaluminum and said portion of water therein, and causing a concentrationof NaOH in said aqueous solution to oscillate equal amounts up and downin response to said rate of consumption of said portion of water in saidstep of reacting and volumes of water added in said step of addingadditional portions of water, respectively.
 13. The process as claimedin claim 12, wherein said aqueous solution contains NaOH at aconcentration between 1.2 M and 19 M NaOH.
 14. The process as claimed inclaim 12, further comprising the step of accumulating precipitate in abottom portion of said vessel, and said step of adding additionalportions of water comprises the step of passing said additional portionsof water through said precipitate.
 15. The process as claimed in claim12, wherein said step of reacting said portion of aluminum with saidportion of water is carried out at a temperature between 4° C. and 170°C.
 16. The process as claimed in claim 15, wherein said step of addingadditional portion of water is carried out when a temperature in saidsolution has reached a peak or 75° C.